title: Long-term effects of cocaine experience on neuroplasticity in the nucleus accumbens core of addiction-prone rats.
abstract: Repeated exposure to drugs of abuse is associated with structural plasticity in brain reward pathways. Rats selectively bred for locomotor response to novelty differ on a number of neurobehavioral dimensions relevant to addiction. This unique genetic animal model was used here to examine both pre-existing differences and long-term consequences of repeated cocaine treatment on structural plasticity. Selectively bred high-responder (bHR) and low-responder (bLR) rats received repeated saline or cocaine injections for 9 consecutive days. Escalating doses of cocaine (7.5, 15 and 30 mg/kg) were administered on the first (day 1) and last (day 9) days of treatment and a single injection of the intermediate dose (15 mg/kg) was given on days 2-8. Motor activity in response to escalating doses of cocaine was compared on the first and last days of treatment to assess the acute and sensitized response to the drug. Following prolonged cocaine abstinence (28 days), spine density was examined on terminal dendrites of medium spiny neurons in the nucleus accumbens core. Relative to bLRs, bHRs exhibited increased psychomotor activation in response to both the acute and repeated effects of cocaine. There were no differences in spine density between bHR and bLR rats under basal conditions or following repeated saline treatment. However, spine density differed markedly between these two lines following prolonged cocaine abstinence. All spine types were decreased in cocaine-treated bHRs, while only mushroom spines were decreased in bLRs that received cocaine. Changes in spine density occurred specifically near the branch point of terminal dendrites. These findings indicate that structural plasticity associated with prolonged cocaine abstinence varies markedly in two selected strains of rats that vary on numerous traits relevant to addiction. Thus, genetic factors that contribute to individual variation in the behavioral response to cocaine also influence cocaine-induced structural plasticity.
authors.affiliation: Molecular and Behavioral Neuroscience Institute, University of Michigan, Ann Arbor, MI, USA. Electronic address: mwaselus@umich.edu.
authors.forename: M
authors.initials: M
authors.lastname: Waselus
authors.affiliation: Molecular and Behavioral Neuroscience Institute, University of Michigan, Ann Arbor, MI, USA; Department of Psychiatry, University of Michigan, Ann Arbor, MI, USA; Neuroscience Program, University of Michigan, Ann Arbor, MI, USA; Department of Psychology, University of Michigan, Ann Arbor, MI, USA.
authors.forename: S B
authors.initials: SB
authors.lastname: Flagel
authors.affiliation: Neuroscience Program, University of Michigan, Ann Arbor, MI, USA.
authors.forename: J P
authors.initials: JP
authors.lastname: Jedynak
authors.affiliation: Molecular and Behavioral Neuroscience Institute, University of Michigan, Ann Arbor, MI, USA; Department of Psychiatry, University of Michigan, Ann Arbor, MI, USA; Neuroscience Program, University of Michigan, Ann Arbor, MI, USA.
authors.forename: H
authors.initials: H
authors.lastname: Akil
authors.affiliation: Neuroscience Program, University of Michigan, Ann Arbor, MI, USA; Department of Psychology, University of Michigan, Ann Arbor, MI, USA.
authors.forename: T E
authors.initials: TE
authors.lastname: Robinson
authors.affiliation: Molecular and Behavioral Neuroscience Institute, University of Michigan, Ann Arbor, MI, USA; Department of Psychiatry, University of Michigan, Ann Arbor, MI, USA; Neuroscience Program, University of Michigan, Ann Arbor, MI, USA.
authors.forename: S J
authors.initials: SJ
authors.lastname: Watson
mesh_terms: D000818:Animals; D016739:Behavior, Addictive / Q000139:chemically induced*; D001522:Behavior, Animal; D003042:Cocaine / Q000494:pharmacology*; D049229:Dendritic Spines / Q000187:drug effects / Q000473:pathology*; D008124:Locomotion / Q000187:drug effects; D008297:Male; D009043:Motor Activity / Q000187:drug effects; D009473:Neuronal Plasticity / Q000187:drug effects*; D009714:Nucleus Accumbens / Q000166:cytology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D013997:Time Factors
chemical_list: D003042:Cocaine
keywords: addiction; cocaine; dendrites; prolonged abstinence; psychomotor sensitization; spine density